For constructing a liquid crystal display (LCD), two transparent substrates are disposed parallel to each other in such a way that the surfaces thereof, on which the respective pixel electrode and common electrode are configured, are facing to each other, while a liquid crystal layer is sandwiched therebetween. Among the LCDs, the active-matrix LCD adopts a matrix of pixel electrodes to display the pixels, and therein switch devices are arranged in the vicinity of each pixel electrode on the transparent substrate, for switching on and off the respective pixel electrodes.
With reference to FIG. 6, the structure and operation of a conventional low temperature polysilicon liquid crystal display (LTPS LCD) are schematically shown. As shown in FIG. 6, the liquid crystal (LC) panel 1 is an active-matrix LC panel having a plurality of pixel electrodes 30, a plurality of scan lines 31, a plurality of data lines 32, a plurality of switching devices 33 and a plurality of reference electrodes 34.
The pixel electrodes 30 are arranged in columns and rows forming a matrix. There are p scan lines 31 arranged along the row direction of the LC panel 1 for selecting the pixels in the same direction, while q data lines 32 are arranged along the column direction of the LC panel 1 for transmitting an applied voltage, which is corresponding to the data to be displayed, to the pixels in the same row direction. The switching devices 33 function for transmitting the data of data lines to the pixels of LC cells through the scanning signals, and are constructed by such as thin film transistors (TFTs). The reference electrodes 34 supply a common voltage level to the respective LC cell located between a set of pixel electrode 30 and reference electrode 34. The LC cell located between a set of pixel electrode 30 and reference electrode 34 is termed as a pixel.
The LC cell utilizes the voltage applied between the pixel electrode 30 and the reference electrode 34 to adjust the light. While the pixels are regularly divided into R, G and B pixels, and the color filters R, G and B are correspondingly arranged at the reference electrodes 34, a color image composed of R, G and B pixels can be displayed. Accordingly, the data lines 32 can be divided to correspond to the R, G and B data based upon the arrangement of R, G and B pixels.
The gate drive circuit 2 functions to apply P scanning signals X1, X2, . . . , Xp subsequently to the scan lines 31 in the LC panel 1. The source drive circuit 3 functions to output the display data as pixel signals Y1, Y2, . . . , Yq, so as to correspondingly generate an applied voltage level for the data lines 32 in the LC panel 1. The signal processing circuit 4, i.e. the control circuit, provides the gate drive circuit 2 and the source drive circuit 3 with a control signal when an external image signal is input and the display data is output to the source drive circuit 3.
The display operation of the LC panel 1 is illustrated as follows. The gate drive circuit 2 is controlled by a control signal from the signal processing circuit 4. The signal processing circuit 4 also supplies scanning signals to any column of scan lines 31. In this case, the switch devices 33 in one column are switching to ON state, and each row of data lines 32 as well as pixel electrodes 30 corresponding to this column are conducted. Data for each row of pixels corresponding to a column of scan lines 31, is supplied to the source drive circuit 3 from the signal processing circuit 4 in advance. Besides, while the switch devices 33 are switching to ON state, the display data is transferred, by the source drive circuit 3, as an applied voltage for each pixel electrode 30 to output. In addition, by scanning from the top column (i=1) to the foot column (i=p) of scan lines 31 of the LC panel 1, the signal processing circuit 4 supplies the display data to all the pixel electrodes 30.
Such conventional gate drive circuit has a layout width of 700˜1000 μm. Since the gate drive circuit is arranged at the periphery of a display device, the arrangement of further circuits would be limited, or the display area of the display device may be reduced owing to the space occupied by the gate drive circuit. For the small-sized portable display device, it is a critical issue to reduce the space occupied by the periphery circuits since a relatively large space thereof does bring a considerable disadvantage therefor.
For example, the gate drive circuits constructed by the shift registers as disclosed by U.S. Pat. No. 6,052,426 and by U.S. Pat. No. 6,064,713 are schematically shown in FIGS. 7 and 8, respectively. It may be possible to adopt such conventional gate drive circuits in an LTPS LCD. Nevertheless, the space occupied by the mentioned circuits and thus the total space are quite considerable since those circuits adopt more than two capacitors therein.